The present invention relates to a mechanical quantity sensor element making use of a stress-magneto effect of noncrystalline magnetic alloys (amorphous magnetic alloys).
Among the mechanical quantity sensors for measuring a force, a torque or the like, a sensor making use of a stress-magneto effect of noncrystalline magnetic alloys has been marketed in recent years. This type of mechanical quantity sensor affords the advantages that (1) non-contact sensing of a force is possible, (2) conversion of a force into an electrical quantity can be achieved directly, (3) a device structure of the sensor is simple and hence reduction in size thereof can be realized, and (4) noncrystalline magnetic alloys are materials having a high strength and a high stiffness, which are perfect elastic materials and exhibit excellent corrosion resistance, and therefore, are excellent in resisting environmental conditions and withstanding a wide scope of working conditions.
By way of example, as shown in FIG. 1, there is known a torque sensor in which a thin belt (ribbon) 01 made of noncrystalline magnetic alloy having positive magneto-striction, that is sensitive in a stress-magneto effect, is wrapped around a rotary shaft 02 so that "torsion strain" generated in the rotary shaft 02 by a torque T may be introduced into the thin belt 01, change of magnetic characteristics of the thin belt 01 caused by the stress-magneto effect is sensed, and thereby the torque T can be sensed. In noncrystalline magnetic alloy having positive magnetostriction, there occurs a phenomenon that if a tensile stress is applied to that alloy, magneto-elastic energy in the direction of the tensile stress is lowered and in that direction magnetization becomes easy. This phenomenon is called stress-magneto effect. In the above-mentioned torque sensor, a uniform easy magnetization axis (uniaxial magnetic anisotropy) Ku in the direction making an inclination angle .alpha.(.alpha.&gt;45.degree.) with respect to the circumferential direction 03 is given to the entire surface of the thin belt 01 by making use of this stress-magneto effect. However, if a torque T is exerted upon the rotary shaft 02, then as shown in FIG. 2, a stress .alpha. represented by the equation of ##EQU1## (where d represents an outer diameter of the rotary shaft 02) is generated in the direction making an angle of .+-.45.degree. with respect to the axial direction of the rotary shaft 02, hence uniaxial magnetic anisotropy is induced also in the direction of +.sigma. due to the stress-magneto effect, and as a result, a combined easy magnetization axis Ku' is given.
Now, on the basis of the fact that generally a magnetic permeability of a magnetic body would vary depending upon a direction of an easy magnetization axis relative to a direction of a magnetic field, the above-mentioned change of the easy magnetization axis (Ku.fwdarw.Ku') is acknowledged as a variation of a magnetic permeability, and thereby a magnitude of the torque T can be detected.
Therefore, if the variation of the magnetic permeability (or a magnetic flux density) is detected as a voltage variation, for example, by means of a magnetizing coil (primary coil) and a detecting coil (secondary coil), a torque-output curve as shown in FIG. 3 can be obtained.
However, n the case of the normally used noncrystalline magnetic alloy, since a linearity of the torque-output curve is poor and a detectable range I for the mechanical quantity is narrow, the sensor element is limited to utilization as a sensor element in a low torque range. Also, since a stress-output curve of the noncrystalline magnetic alloy has a large gradient in the proximity of stress=0 as shown in FIG. 4, a sensitivity at that portion is very high. Therefore, in combination with the fact that the stress distribution produced in the thin belt 01 by uneven bonding forces upon bonding the thin belt 01 onto the surface of the rotary shaft 02 (as shown in FIG. 1) is not uniform, in the case where the torque exerted upon the rotary shaft 02 is zero, the sensor output which should be inherently zero, would be detected as a relatively large value because of difference in the stopping angle of the rotary shaft 02.
In addition, in the case of producing a thin belt of noncrystalline magnetic alloy through a liquid super-quenching process, as it is impossible to perform quenching under a uniform cooling condition over the entire surface of the thin belt or under an always uniform cooling condition, generation of non-uniform residual stress is inevitable. So when a plurality of obtained thin belts are used as mechanical quantity sensor elements, a disadvantage is associated that "distribution" of magnetic characteristics caused by difference of residual stress would be generated.